The invention relates to method and apparatus for securing an end cap within a chromatography cartridge.
Liquid column chromatography is a technique for identifying, separating, or purifying individual components in a subject sample. In employing the technique, a xe2x80x9cstationary phase,xe2x80x9d such as a surface active powder, is packed into a chromatography column to form a chromatography media bed. A xe2x80x9cmobile phasexe2x80x9d consisting of a carrier liquid and a sample to be identified, analyzed, or purified is passed through the column. Different compounds in the sample migrate through the column at different rates, depending, e.g., on their size and degree of attraction to the stationary phase in the column. Consequently, the different compounds in the liquid emerge from the column at different times, allowing separation of the compounds in the sample. For a description of column chromatography, see McDonald et al., U.S. Pat. No. 4,250,035, entitled xe2x80x9cRadial Compression of Packed Beds,xe2x80x9d incorporated herein by reference.
Liquid column chromatography can be carried out using a disposable cylindrical cartridge. The cartridge contains the media bed bounded axially at both ends by an end cap. The end caps are secured firmly within the cartridge to axially support the media bed. Known methods of securing the end caps include threading and the use of pre-formed retention grooves.
In general, in one aspect, the invention features a method of forming a chromatography cartridge including providing a flexible-walled tube, placing a first end cap within the tube in sealing engagement with a wall of the tube, forming a media bed within the tube supported by the first end cap, cooling a second end cap to thermally contract the second end cap to a dimension less than an inner dimension of the tube, placing the second end cap within the tube and against the media bed, and sealing the second end cap to the tube wall by thermal expansion of the second end cap upon warming. The expansion of the second end cap causes the tube wall to deform.
Embodiments of this aspect of the invention may include one or more of the following features. The first end cap is cooled prior to placing the first end cap within the tube and the first end cap is sealed to the tube wall by thermal expansion of the first end cap upon warming. The expansion of the first end cap causes the tube wall to deform.
The tube wall has an inner surface which defines a section of constant inner diameter for slidably receiving the second end cap.
According to another aspect of the invention, a method of supporting a media bed in a chromatography cartridge tube includes cooling an end cap to thermally contract the end cap to a dimension less than an inner dimension of the tube, placing the contracted end cap within the tube and against the media bed, and sealing the end cap to the tube by thermal expansion of the end cap upon warming. The expansion of the end cap causes the tube to deform.
Embodiments of this aspect of the invention may include one or more of the following features.
The end cap is cooled with liquid nitrogen.
In an illustrated embodiment, the tube and the end cap are cylindrical and cooling the end cap thermally contracts the end cap to a diameter less than an inner diameter of the tube. Expansion of the end cap causes, e.g., about a 1 to 10 percent, preferably about a 2 percent, increase in the inner diameter of the tube. The end cap has, at room temperature, a diameter of, e.g., about 1 to 10 percent, preferably about 2 to 4 percent, larger than the inner diameter of the tube. The cooling step contracts the end cap to a diameter of, e.g., about 0.1 to 1 percent less than the inner diameter of the tube.
The tube is formed from a polymeric material, and the end cap is formed from a polymeric material or a metal. Alternatively, the tube and the end cap are both metal.
The end cap includes a flow distributor and a sieve.
According to another aspect of the invention, a chromatography column assembly includes a flexible-walled tube for containing chromatography media, and an end cap for positioning within the tube. The end cap, at a first temperature, has a first dimension greater than an inner dimension of the tube. The end cap is configured such that upon cooling to a second temperature lower than the first temperature, the end cap thermally contracts to a second dimension less than the inner dimension of the tube permitting placement of the end cap within the tube. Upon warming, the end cap expands to deform the tube to seal the end cap against the tube.
According to another aspect of the invention, a chromatography column includes a flexible-walled tube containing chromatography media, and an end cap positioned within the tube. The end cap has a dimension greater than an inner dimension of the tube such that the tube is locally deformed by the end cap in a region in which the end cap is positioned to secure the end cap within the tube. The end cap is configured to thermally contract upon cooling to a dimension less than the inner dimension of the tube to permit placement of the end cap within the tube.
Embodiments of the invention may include one or more of the following advantages. The end cap can be fixed at any height within the cartridge as dictated by the height of the media bed. The intimate seal between the end cap and wall of the tube limits build-up of debris between the end cap and tube wall.